The present invention concerns a package strapper. Three motor-driven mechanisms, specifically a strap feed, a strap stretcher, and a strap-end fastener, are mounted on a strap track. The track loops around the package. The feed includes at least two wheels, each forced against one side of the strap by a spring. The motor that drives the feed can be reversed. The strap-stretcher wheel is between the feed and the track and is partly loosely surrounded by a strap guide. One end of the guide opens into the track.
To ensure high performance on the part of the package strapper, the incoming strap rapidly occupies the entire loop of the track. The strap-feed motor turns off in accordance with a known principle when the leader, the forward end of the strap, that is, encounters a switch at the end of the track. The motor's inertia, however, allows it to feed enough extra strap to jam the track. The motor must accordingly also be mechanically lifted away from the feed wheels by an expensive magnetic clutch, which eventually wears out and must be replaced. Another drawback is that the leader tends to rebound off the switch and buckle the length of strap behind it.
The tensions in the looped strap are evened out in accordance with a known principle. Specifically, the strap-stretcher motor is loosely mounted and, as its reaction increases, forces a spring back slightly against a bearing and engages a switch. The switch turns off the motor and engages a magnetic clutch, which immediately disengages the still spinning motor from the drive. The tension on the spring can be adjusted, and hence the tension in the strap as well. The strap-tension motor accordingly also requires an expensive clutch that wears out. Finally, the spring's bearing against the switch is also complicated.
The object of the present invention is accordingly to improve a package strapper of the aforesaid genus to the extent that the clutch or similar wear-subject component can be eliminated, the leader will not slam against the switch, and the strap-stretcher motor will generate precisely reproducible tension in the strap by strictly electrical means and without any mechanical components that are subject to wear.